This invention relates generally to electromagnetic valves, and more particularly to a pilot-controlled electromagnetic two-way valve which can be operated reliably by means of a solenoid of a small size irrespective of the conditions of pressure differential existing between the fluid on the primary and secondary sides of the valve.
It is known to provide pilot control means in electromagnetic valves as an expedient to lessen the burden which would be imposed on the solenoid in operations under high pressure conditions. The pilot-controlled electromagnetic or solenoid-operated valves which operate even under conditions of zero pressure differential are also known, for example, from U.S. Pat. No. 3,208,716. In the conventional electromagnetic valves of the class mentioned, a valve or closure means for opening and closing a pilot fluid passage is usually provided on a core plunger of the solenoid to open the pilot valve directly by the action of the core plunger. Actuation of the electromagnetic valve operating means or solenoid takes place when the core plunger is in its lowest position distant from a fixed core or plug of the solenoid. This means that it is necessary to employ a solenoid device of a large size to cope with operations involving great pressure differentials between the fluid on the primary and secondary sides of the valve, due to the particular magnetic attraction characteristic of the solenoid that the magnetic pull on the core plunger is weak at the lowest position remote from the fixed core and increases as the plunger approaches the fixed core or plug.